RF (radio frequency) power architectures within the telecommunications field focus on achieving high DC-to-RF efficiency at significant power back-off from Psat (the average output power when the amplifier is driven deep into saturation). This is due to the high peak to average ratio (PAR) of the transmitted digital signals, such as W-CDMA (wideband code division multiple access), LTE (long term evolution) and WiMAX (worldwide interoperability for microwave access). The most popular power amplifier architecture currently employed is the Doherty amplifier. The Doherty amplifier uses a class AB main amplifier and a class C peaking amplifier, and efficiency is enhanced through load modulation of the main amplifier from the peaking amplifier.
If high efficiency at a high output back-off (OBO) is required, a highly asymmetric ratio between the size of main and peaking amplifiers is typically required. However, such an asymmetry requirement limits the maximum RF output power that can be obtained from such a design. A 3-way Doherty amplifier can also be used to operate at more than 6 dB from the peak output power, i.e., at more than 6 dB OBO. However, three-way Doherty amplifiers are complicated and have a long design process, lack performance consistency, and require a larger physical layout. Neither of the aforementioned approaches allow for dynamic load modulation. An architecture called ‘envelope tracking’ or ‘drain modulation’ can also be used to provide high efficiency at more than 6 dB OBO, but this approach requires very significant system redesign and additional complexity.